—radius /ˈreɪ.di.əs/
noun [C] (PLURAL radii) (DISTANCE)
F0 (the length of) a straight line joining the centre of a circle to its edge or the centre of a sphere to its surface:
» The radius of this wheel is 30 cm.» This wheel has a radius of 30 cm.Thesaurus+: ↑Parts of geometrical shapesF0 a distance:
» The station, shopping centre and school lie within a one-mile radius of the house.Thesaurus+: ↑Measurements in generalnoun [C] (PLURAL radii) SPECIALIZED (BONE)
► F0 the thicker of the two bones in the lower armSee picture: radius 
Thesaurus+: ↑The armThesaurus+: ↑Bone structures